Polyurethane has good mechanical strength and elasticity, is therefore widely used in various applications such as coating agents, molding materials, paints, and optical films, and is actively studied as materials for moisture-permeable waterproof fabrics and synthetic leathers.
However, a synthetic leather coated with polyurethane is inferior in moisture permeability and has a drawback in that moisture persists during wearing of the polyurethane-coated synthetic leather. One method proposed to address the drawback is to subject a polyurethane resin solution to wet coagulation to form a porous body (see, for example, PTL 1). However, to perform the wet coagulation, a special device and a complicated processing process must be used.
One proposed easily processable way is a hydrophilic urethane film that is applicable to dry lamination (see, for example, PTL 2). However, since the technique for this hydrophilic urethane film uses highly water-absorbent polyoxyethylene glycol as a main component, a problem arises in that the film swells when in contact with water during actual use and undergoes a change in appearance or is separated from a substrate. Another problem with the hydrophilic urethane film is that its lightfastness, heat resistance, etc. are poor because the ether group concentration is high, and it is therefore difficult to use the film for furniture and vehicle applications that require durability.